This commit introduces the PotionEffectThing and associated parser. The parser simply delegates to the existing PotionEffectParser utility class the same way the ItemStackThing parser does it. To distinguish potion effects from other things, the parser requires a prefix of "effect:".
As with the initial Thing API commit, this commit also adds an overload to the existing parser class to avoid spamming the console with meaningless warnings.
Andreas Troelsen
a2e235e77a